IMO Cars are absolutely irrelevant, tracks are what counts.
F355 Challenge remains game with greatest car-to-track ratio ever, with only 1 car and 10 tracks (11 with test-track) and there was no single problem with that.
As long as car selection covers all basic variations of configuration/drive-type/power, there is no problem. And approx. 20-30 cars are more then enough for that IMO
Of course, cars - especially particular models/marquees - are *important* to marketing for mainstream audience, as we have learned through time. However, even the current pCARS selection of vehicles is more then enough to satisfy all basic types of cars today. For me personally the tracks (courses) are the single greatest fundament of pCARS and I am glad how SMS is so focused on their development.
This.